1. Field of the Invention
This invention relates to a spring clutch device which utilizes wrapped springs and more particularly to a spring clutch device which is capable of cutting off transmission of a driving force at a desired point.
2. Description of the Prior Art
There has been known so-called spring clutches of the type in which, for example, a coil spring is wound around the outer circumference of a driving shaft in close contact therewith with one end of the spring being attached to a driven member which is disposed concentrically with the driving shaft and being arranged to be driven thereby. In such a device, only the rotation of the driving shaft in the direction of tightening the coil of the spring by a frictional force between the driving shaft and the spring is transmitted to the member to be driven. The rotation of the driving shaft in the reverse direction, i.e. a direction in which the inner diameter of the spring coil is widened, is arranged not to be transmitted to the member to be driven.
Further, there has been also known a spring clutch having a change-over lever for effecting change-over between a condition wherein the rotation of a driving shaft is transmitted in one direction and a condition wherein the rotation is not transmitted. In such a device, a projection is provided at one end of a spring of the above stated type and a change-over lever is arranged to be engaged with the projection. In a conventional spring clutch of this type, transmission of rotation of the driving shaft is arranged to be cut off when the change-over lever engages the projection.
A spring clutch arranged in this manner has the advantage that the change-over operation of the clutch can be accomplished very simply by operation of the change-over lever. On the other hand, however, release from the clutch transmission state is allowed to be effected only once per rotation of the shaft of the clutch. In other words, it is impossible to cut off the clutch at any desired phase of rotation thereof.